TROPICAL REGIONAL PRECIPITATION ANOMALIES: Global warming and El Niño cases

Transcription

1 TROPICAL REGIONAL PRECIPITATION ANOMALIES: Global warming and El Niño cases J. David Neelin *, Hui Su * and Chia Chou ** * Dept. of Atmospheric Sciences & Inst. of Geophysics and Planetary Physics, U.C.L.A., ** Inst. of Earth Sciences, Academia Sinica, Taiwan Tropical regional precipitation anomalies associated with changes in deep convection zones: including drought regions in global warming case; mechanisms?; any similarities in El Niño case? Intermediate complexity climate model QTCM (Quasi-equilibrium Tropical Circulation Model)

2 Observed anomalies during July-Nov 1997 Precipitation (mm/day) Tropospheric Temperature

3 QTCM anomalies forced by Pacific positive SST anomalies July-Nov 1997 Precipitation (mm/day) Tropospheric Temperature

4 QTCM July-Nov 1997: Anomaly budget contributions1 Moisture convergence M q v (by divergent flow) Moist static energy divergence * M v * Gross moist stability M=M s M q is an effective stability that includes partial cancellation of adiabatic cooling by diabatic heating

5 QTCM July-Nov 1997: Anomaly budget contributions2 Radiative cooling anom. (top of atmosphere) due to temp. anom. Mean wind advection of moisture anomaly v q '

6 ENSO teleconnections to regional precip.. anomalies

7 ENSO teleconnections to regional precip.. anomalies a small zoo of mechanisms with moist convective and cloud radiative feedbacks

8 QTCM experiments suppressing various mechanisms Precipitation Anomalies Control Anomaly ( ) ' term suppressed in region: (v q) ' T ' contribution to CAPE

9 GCM Precip. Anom.. Dec-Feb Global warming case precipitation anom. Greenhouse gas scenarios for rel. to clim

10 QTCM doubled CO 2 experiments Qflux mixed-layer ocean Dec - Feb Precip change Dec - Feb QTCM Precip climatology

11 QTCM doubled CO 2 experiments Moisture budget contributions1 M q' v Anomalous moisture convergence due to moisture anom. q ' (v q) ' Anomalous moisture advection

12 QTCM doubled CO 2 experiments Moisture budget contributions2 M q v ' Anomalous moisture convergence due to anomalous divergence (feedback)

13 The upped-ante mechanism1 Margin of convective zone with v inward from dry region

14 The upped-ante mechanism2 Margin of convective zone with v inward from dry region

15 Anomalous Gross Moist Stability (M ' ) mechanism Moist static energy transport by divergent flow M v M=M s -M q increases with increasing moisture, tends to reduce M may partially compensate if cloud top rises M v ' + M ' v = F ' net - (v q) ' + reduced increases to compensate M q P ' v(-m ' ) M Mechanism increases convergence & precip. in strong convergence zones: rich-get-richer

16 QTCM 2xCO 2 Expt.. suppressing change in moisture advection (testing the upped-ante mechanism) Experiment 2xCO 2 Precip. change (mm/day) Control 2xCO 2 Precip. change

17 QTCM 2xCO 2 Expt.. suppressing change in gross moist stability, M (testing the M ' mechanism) Experiment 2xCO 2 Precip. change (mm/day) Control 2xCO 2 Precip. change

18 Summary analysis of tropical regional precipitation anomalies in ENSO teleconnection case a handful of contributing mechanisms 2XCO 2 case, mixed-layer ocean case set of mechanisms with some cross-over to ENSO case the "upped-ante mechanism": contributes substantial negative precipitation anomaly regions in both cases drought occurs at margins of convection zones with climatological wind inflow from dry zone into convection zone the "anomalous gross moist stability (M') mechanism": contributes positive precipitation changes in strong precipitation regions in global warming case (rich-get-richer) but theory for M' is very poor caveat Tropical mean precipitation anomaly mechanisms appear to differ between ENSO and global warming cases

19 Summary analysis of tropical regional precipitation anomalies in ENSO teleconnection case a handful of contributing mechanisms 2XCO 2 case, mixed-layer ocean case set of mechanisms with some cross-over to ENSO case the "upped-ante mechanism": contributes substantial negative precipitation anomaly regions in both cases drought occurs at margins of convection zones with climatological wind inflow from dry zone into convection zone the "anomalous gross moist stability (M') mechanism": contributes positive precipitation changes in strong precipitation regions in global warming case (rich-get-richer) but theory for M' is very poor caveat Tropical mean precipitation anomaly mechanisms appear to differ between ENSO and global warming cases

20 MOIST DYNAMICAL FEEDBACKS IN TROPICAL CLIMATE SENSITIVITY: ENSO vs. Global warming J. David Neelin *, Hui Su * and Chia Chou ** * Dept. of Atmospheric Sciences & Inst. of Geophysics and Planetary Physics, U.C.L.A., ** Inst. of Earth Sciences, Academia Sinica, Taiwan Tropical regional precipitation changes associated with shifts of or anomalies within deep convection zones: mechanisms for ENSO case; any similarities in global change case? Intermediate complexity climate model QTCM (Quasi-equilibrium Tropical Circulation Model)

21 TROPICAL PRECIPITATION ANOMALIES: ENSO TELECONNECTIONS VS. GLOBAL WARMING J. David Neelin *, Hui Su * and Chia Chou ** * Dept. of Atmospheric Sciences & Inst. of Geophysics and Planetary Physics, U.C.L.A., ** Inst. of Earth Sciences, Academia Sinica, Taiwan Tropical regional precipitation changes associated with shifts of or anomalies within deep convection zones: any similarity of mechanisms for ENSO and global change cases? Intermediate complexity climate model QTCM (Quasi-equilibrium Tropical Circulation Model)